1. Field of the-Invention
The present invention relates generally to a device and a method for transmitting a downlink/uplink control channel in CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a device and a method for transmitting a downlink/uplink control channel, which provide compatibility between an HSDPA (High Speed Downlink Packet Access) mobile communication system and a non-HSDPA mobile communication system.
2. Description of the Related Art
Mobile communication systems have been developed to additionally provide high-speed, high-quality packet data for data service or multimedia service as well as voice service. The 3rd generation mobile communication systems, which are divided into asynchronous ones (3GPP) and synchronous ones (3GPP2), are being standardized to realize high-speed, high-quality wireless data packet services. For example, HSDPA is undergoing standardization within the 3GPP and the 1×EV/DV within 3GPP2. Efforts to find ways to provide high-quality wireless data packet services at a data rate of 2 Mbps or higher have driven these standardization activities, and the 4th Generation mobile communication systems will be designed to provide higher-speed, higher-quality multimedia services.
HSDPA requires advanced technology improving the capability of adapting to channel conditions beyond the technology needed to implement the existing mobile communication systems. The following three schemes have been introduced to HSDPA to support high-speed packet transmission.
(1) Adaptive Modulation and Coding Scheme (AMCS): A modulation and coding scheme (MCS) for a data channel is determined according to the channel condition between a cell and a user, thus increasing the overall use efficiency of the cell. The MCS is a combination of modulation and coding schemes and there are defined a plurality of MCSs numbering level 1 to level n. The AMCS is an optimum MCS chosen among the MCSs according to the channel status between the cell and the user.
(2) N-channel Stop and Wait Hybrid Automatic Re-transmission Request (n-channel SAW HARQ): This is a kind of HARQ. In conventional ARQ, an ACK (acknowledgment) signal and a retransmission packet are exchanged between a UE and a node B controller, while in HADPA, the exchange occurs between the UE and a high-speed downlink shared channel (HS-DSCH) in the MAC layer of the node B. Another feature of the n-channel SAW HARQ is that when an ACK signal not received, a plurality of packets can be transmitted on n logical channels. The node B does not transmit the next packet until it receives an ACK signal for the previous transmitted packet from the UE in typical Stop and Wait ARQ. In other words, the node B must await the ACK signal although it can transmit the next packet. On the contrary, in the n-channel SAW HARQ the node B can transmit a plurality of next packets successively even if it does not receive the ACK signal for the previous transmitted packet, thereby increasing channel use efficiency. That is, if n logical channels are established between the UE and the node B and those logical channels can be identified by their channel numbers or their transmission time, the UE can determine on what channel a packet is received at some point in time and also rearrange received packets in the right reception order.
(3) Fast Cell Selection (FCS): The FCS scheme allows an HSDPA UE in a soft handover region (SHR) to receive packets from only a cell in the best channel condition, so that the overall interference is reduced. If another cell exhibits the best channel condition, the UE receives packets from the cell on an HS-DSCH with minimum communication interruption.
Due to the introduction of the new schemes above, new control signals are configured between the UE and the node B in HSDPA. For AMCS, the UE reports the channel condition between the UE and the node B. The node B then notifies the UE of an MCS level determined based on the channel condition. For n-channel SAW HARQ, the UE transmits an ACK/NACK (Negative Acknowledgment) signal to the node B. For FCS, the UE transmits a signal indicating the best cell to a node B that offers the best-quality channel. If the best cell is changed, the UE reports its packet reception status to the new best station. Then, the new best node B provides necessary information to aid the UE in selecting the best cell correctly.
As described above, since additional related information is required for supporting HSDPA, different UL-DPCH (Uplink Dedicated Physical Channel) structures are adopted depending on whether HSDPA is supported or not.
A description will first be made of a conventional UL-DPCH structure not supporting HSDPA. FIG. 9 illustrates the frame structure of the conventional UL-DPCH when HSDPA is not supported.
Referring to FIG. 9, one UL-DPCH frame is comprised of 15 slots, from slot #0 to slot #14. The UL-DPCH contains the UL-DPDCH (Uplink Dedicated Physical Data channel) and the UL-DPCCH (Uplink Dedicated Physical Control Channel). The UL-DPDCH carries higher-layer frame data to a node B in each slot. The UL-DPCCH carries control information such as a pilot symbol, TFCI (Transport Format Combination Indicator) bits, an FBI (Feedback Information) symbol, and a TPC (Transmit Power  Control Commander) symbol in each slot. The pilot symbol is a channel estimation signal by which uplink data is demodulated. The TFCI bits indicate in what TFC channels are transmitted for the duration of the current frame. The FBI symbol transmits feedback information in the case of transmit diversity. The TPC symbol is used to control downlink transmission power. The UL-DPCCH is spread with an SF=256 orthogonal code all the time. SF represents a spreading factor.
The above-described UL-DPCCH cannot transmit necessary information if HSDPA is supported. Therefore, a novel UL-DPCCH should be configured for HSDPA. FIG. 10 to FIG. 11D illustrate conventional UL-DPCCH structures for support of HSDPA.
FIG. 10 illustrates a conventional UL-DPCCH supporting HSDPA, which is a modification to the UL-DPCCH illustrated in FIG. 9. Referring to FIG. 10, an SF=128 orthogonal code is applied to the UL-DPCCH so that more bits (20 bits) can be transmitted at the same chip rate in each slot than in the UL-DPCCH illustrated in FIG. 9. As a result, the UL-DPCCH carries HSDPA control information as well as UL-DPDCH control information. Each slot is the same in structure in an UL-DPCCH frame. In each slot, the UL-DPCCH carries ACK bits and Meas bits in addition to the pilot symbol, the TFCI bits, the FBI symbol, and the TPC symbol illustrated in FIG. 9. The ACK bits indicate whether an error has been detected in received downlink HSPA data and the Meas bits indicate the downlink channel condition measured at the UE to determine an appropriate MCS level in the node B.
FIG. 11A to FIG. 11D illustrate the structure of another conventional UL-DPCCH supporting HSDPA, which is another modification to the UL-DPCCH illustrated in FIG. 9. Referring to FIG. 11A to FIG. 11D, an SF=128 orthogonal code is applied to the UL-DPCCH so that more bits (20 bits) can be transmitted at the same chip rate in each slot than in the UL-DPCCH illustrated in FIG. 9. As a result, the UL-DPCCH can carry HSDPA control information as well as UL-DPDCH control information. Unlike the slot structure illustrated in FIG. 10, however, the UL-DPCCH adopts different slot structures within each TTI (Transmission Time Interval) having three slots. Thus, the UL-DPCCH carries control information in time division. In FIG. 11A, the UL-DPCCH delivers only UL-DPDCH control information in a TTI. In FIG. 11B, the UL-DPCCH delivers HSDPA control information in the first two slots and UL-DPDCH control information in the last slot of the TTI. In FIG. 11C, the UL-DPCCH delivers UL-DPDCH control information in the first two slots and ACK/NACK information in the last slot of the TTI. In FIG. 11D, the UL-DPCCH delivers HSDPA control information excluding ACK/NACK in the first two slots and the ACK/NACK information in the last slot of the TTI. As seen from FIG. 11A to FIG. 11D, each slot in a TTI may have a different structure, if necessary. This variable slot structure allows the node B to determine whether to retransmit HSDPA data by processing the ACK/NACK information and prepare substantially for retransmission because the UL-DPCCH carries the ACK information in one slot of a TTI and the remaining HSDPA control information or the UL-DPDCH control information in the other slots of the TTI.
When both the node B and the UE support HSDPA, they know the UL-DPCCH structure illustrated in FIG. 10 or FIG. 11A to FIG. 11D. On the contrary, when both the node B and the UE do not support HSDPA, the UL-DPCCH structure illustrated in FIG. 10 or FIG. 11A to FIG. 11D is not available. For example, if the node B does not provide an HSDPA service, it cannot receive the UL-DPCCH illustrated in FIG. 10 or FIG. 11A to FIG. 11D.
Meanwhile, the UE may enter an SHR in which the coverage areas of an HSDPA node B and a non-HSDPA node B overlap. In the soft handover situation, the UL-DPCCH structure illustrated in FIG. 10 or FIG. 11A to FIG. 11D is not known to the non-HSDPA node B. As a result, the node B cannot receive UL-DPDCH control information.
Accordingly, there is a need for designing an UL-DPCCH in such a way that even the non-HSDPA node B can receive control information from the HSDPA UE. In other words, the aim of designing the UL-DPCCH is to offer compatibility between the HSDPA UE and the non-HSDPA node B.
To support HSDPA, the node B should transmit the following control information to the UE.
1) HSDPA indicator (HI): this indicates whether there exists HSDPA data destined for the UE.
2) MCS level: the MCS level indicates a modulation and channel coding scheme used for an HS-DSCH.
3) HS-DSCH channelization code: the channelization code of an HS-DSCH used for the UE.
4) HARQ process number: this indicates on which logical channel a particular packet is transmitted when using n-channel SAW HARQ.
5) HARQ packet number: the number of a downlink data packet known to the UE so that the UE can report an HSDPA data reception state to a new best cell if a best cell is changed in FCS.
Besides the above control information, the node B transmits an uplink transmission power offset value to the UE so that the UE can transmit information indicating a selected best cell to neighboring nodes B using the uplink transmission power offset value.
FIG. 16 illustrates the structure of a conventional DL-DPCH (Downlink Dedicated Physical Channel) specified in the 3GPP Release 99 (R-99) specification for an existing non-HSDPA mobile communication system. Referring to FIG. 16, the DL-DPCH carries data needed support the operation of a higher layer or dedicated service data, like voice, in a first data field Data1 and a second data field Data2. A TPC field transmits a downlink transmission power control command by which uplink transmission power is controlled, a TFCI field transmits information about the TFC of the first data field Data1 and the second data field Data2, and a pilot field has a preset pilot symbol sequence by which the UE estimates downlink channels.
The DL-DPCH structure of FIG. 16 defined by Release 99 cannot provide an HSDPA service to the UE. Accordingly, there is a need for exploring a novel DL-DPCH structure to support HSDPA. Meanwhile, an HSDPA UE may simultaneously receive data packets on an HS-DSCH from an HSDPA node B and data on a DL-DPCH from a non-HSDPA node B. Therefore, a novel DL-DPCCH for HSDPA should be designed to support the traditional services provided by Release 99 as well as the HSDPA service.
If HSDPA is implemented, HSDPA and non-HSDPA mobile communication systems will inevitably coexist. Therefore, a novel UL-DPCH and a novel DL-DPCH must be defined with compatibility between the HSDPA and non-HSDPA mobile communication systems.